BACKGROUNDSimultaneous determination of thorium and potassium in geological samples can provide an important basis for exploration of radioactive mineral resources and evaluation of the natural radioactive ecological environment. The thorium in geological samples is usually digested by alkali fusion in traditional methods and determined by spectrophotometry. The traditional method is long, complex and not suitable for simultaneous determination of multiple elements. The potassium oxide in geological samples is digested by acid and generally determined by flame atomic absorption spectrometry, which requires diluting the solution with high concentration and has low detection efficiency. The determination of thorium and potassium oxide involves two different analytical methods and analytical instruments.

OBJECTIVESTo establish an analytical method for simultaneous determination of thorium and potassium oxide in geological samples.

METHODSChemical solvent which consists of nitric acid, hydrofluoric acid and perchloric acid, was identified according to the characteristics of the chemical composition of the geological samples. The geological samples were dissolved with this solvent and extracted with nitric acid. The content of thorium and potassium oxide in geological samples was measured by inductively coupled plasma-optical emission spectrometry (ICP-OES) at wavelengths of 401.913nm and 766.490nm, respectively by radial observation mode.

RESULTSThe correlation coefficient of the calibration curve of thorium and potassium oxide was greater than 0.999 and the detection limit of this method was 0.69μg/g and 0.008%, respectively. The measured value of the standard substance was consistent with the identified value, and the absolute logarithmic error of the two values was less than 0.1. The relative standard deviation was less than 6.0% and the recovery ranged from 96.0% to 104.0%.

CONCLUSIONSThis method meets the requirements of the testing quality management standard for geological and mineral laboratories.